Magnetron tube



April 24, 1952 J. H. ENGELMAN 3,031,595

MAGNETRON TUBE Filed Dec. 16, 1959 IN VEN TOR.

JOSEPH H. ENGELMAN A TTORNEY United States Patent 3,031,595 MAGNETRONTUBE Joseph H. Engelman, Paoli, Pa., assignor to Burroughs Corporation,Detroit, Mich., a corporation of Michigan Filed Dec. 16, 1959, Ser. No.859,979 4 Claims. (Cl. 313-157) This invention relates to magnetron-typeelectron discharge tubes and to improvements in the construction of suchtubes, particularly in the portion thereof which produces the magneticfield.

One form of magnetron tube, to which the principles of the inventionapply, includes an electrode assembly which comprises an elongatedcentral cathode and a plurality of groups of elongated electrodessurrounding the cathode and secured together at their opposite ends bymeans of insulating end disks or plates. All of the electrodes aresubstantially parallel to each other. An external cylindrical magnetsurrounds the tube envelope and electrode assembly.

In operation of this type of tube, a beam of current flows from thecentral cathode and is urged to rotate around the tube under theinfluence of crossed electric and magnetic fields. The beam may remainat one group of electrodes indefinitely, or it may be switched fromposition to position by the application of proper potentials to selectedones of the tube electrodes.

It has been found that some of the electrons in the beam from thecathode tend to flow toward the ends of the electrode assembly wherethey strike the insulating end disks which support the electrodes. Thiselectron bombardment of the insulating disks causes them to becomeelectrically charged, with the result that the electric field in thetube becomes distorted and electron flow is adversely aifected.

Another problem inherent in tubes of the type described above resultsfrom the use of the cylindrical magnet. The operation of mounting andsecuring the magnet is comparatively critical since optimum tubeoperation depends on a particular and exact orientation of the magnet.By comparison with other tube operations, the steps of positioning andsecuring the magnet are undesirably time consuming.

In addition, when the tubes are in use, extraordinary care must beexercised to avoid striking the tube and thereby disorienting themagnet. Such disorientation, even though slight, might render the tubeuseless.

The objects of the present invention are concerned with the provision ofan improved construction for a magnetron beam switching tube in whichthe placement of the means for generating the magnetic field is notcritical and, in addition, an improved magnetic field configuration isachieved which provides improved electron beam flow.

In brief, a magnetron-type electron tube embodying the inventioncomprises, in a suitable envelope, an electrode assembly including acentral longitudinally elongated cathode electrode surrounded by groupsof longitudinally elongated electrodes which are adapted to form andreceive an electron beam from the cathode. The various electrodes aresecured together parallel to each other by means of insulating end diskssecured to the opposite ends of the electrodes. In place of theconventional cylindrical permanent magnet surrounding the tube, anassembly of permanent magnet rods spaced apart uniformly and parallel toeach other is provided. The magnet rod assembly is coaxial with theelectrode assembly and may be either outside or inside the tubeenvelope.

The invention is described in greater detail by reference to thedrawing, wherein:

FIG. 1 is a perspective view, partly in section, of a "ice magnetronbeam switching tube embodying the invention;

FIG. 2 is a sectional view of a modification of the tube of FIG. 1; and

FIG. 3 is an elevational view of the tube of FIG. 1 illustrating thegeneral orientation of the magnetic field of the tube.

The principles of the invention are applicable to magnetron tubes and,particularly, to a multi-position Type 6700 magnetron beam switchingtube. This type of tube is cylindrical in form and includes an envelope12 which contains a central longitudinally elongated cathode '14 and tengroups of electrodes spaced radially equidistantly from the cathode andsurrounding the cathode. Each group of electrodes includes a generallyU-shaped elongated spade electrode 16 and a generally L-shaped targetelectrode 18 positioned so that each target occupies the space betweenadjacent spade electrodes. Each spade electrode serves to form and holdan electron beam on its corresponding target electrode. A generallyrod-like switching electrode 20 is also included in each group ofelectrodes and is positioned between one edge of each target electrodeand the adjacent spade electrode. The switching electrodes are known asswitching grids. All of the tube electrodes are secured together bymeans of top and bottom mica disks 22 and 24. The tube 10 also includesmagnet means, to be described, which provides an axial magnetic fieldwhich is utilized in conjunction with electric fields within the tube toform and switch an electron beam from the cathode to each of the groupsof electrodes. The direction in which the beam switches, that isclockwise or counter-clockwise, is always the same and is determined bythe orientation of the electric and magnetic fields.

Briefly, in operation of tube 10, electrons emitted by the cathode areretained at the cathode if each of the spades, targets and switchinggrids carries its normal operating electrical potential. When a spade orswitch ing grid experiences a suitable lowering of its potential, anelectron beam is formed and directed to the corresponding targetelectrode. The electron beam may be switched from one target electrodeto the next by thus suitably altering the electrical potentials of aspade or switching grid. Under normal operating conditions, wheneverelectrode voltages are such that a beam might be supported at severalpositions, the beam switches to the most leading position and locks inat this position.

According to the present invention, magnet means for obtaining thedesired magnetic field in the tube 10 comprises an array of permanentmagnet rods 26 provided surrounding and coaxial with the electrodeassembly. The corresponding magnetic poles of the rods are orientedadjacent to each other. In FIG. 1, the magnet rods are placed outsidethe tube envelope and held in position in any suitable fashion, forexample, by means of insulating rings 30 and 32 which are cemented orotherwise held in place surrounding the tube envelope. Substantially anynumber of magnet rods 26 may be employed, with, for example, one rod foreach group of electrodes being satisfactory.

'In a modification of the invention shown in FIG. 2, the desiredmagnetic field is provided and, in addition, a more compact tubeconstruction is achieved by mounting the magnet rods 26 inside the tubeenvelope 1 2 and surrounding the electrode assembly. The mganet rods maybe supported in any suitable fashion, for example, by having their endsinserted in suitable apertures in the top and bottom mica disks 22 and24. An important advantage of this embodiment of the invention is thatit reduces the size of the tube.

One advantage of the present invention resides in the fact thepositioning of the magnet rods is considerably less critical than thepositioning of a cylindrical magnet surrounding the tube. In addition,the magnet rods seem to provide a magnetic field pattern of the formgenerally indicated by the fiux lines 34 in FIG. 3. The magnetic fluxlines 34 bend toward the center of the elec-, trode cage. Thisconfiguration of magnetic flux lines, in conjunction with the electricfields in the tube, tends to limit an electron beam to the center of thecage and prevents fanning out of a beam to strike the top and bottommica disks.

What is claimed is:

1. A magnetron tube including an envelope, an electrode assembly in saidenvelope, said electrode assembly having a longitudinal axis in saidenvelope and including a central cathode and a plurality of electrodessurrounding said cathode and adapted to receive electron beams from saidcathode, and magnet means providing an axial magnetic field in saidenvelope for controlling the flow of electrons from said cathode to saidelectrodes said magnet means comprising a plurality of spaced-apartrodlike magnets oriented substantially parallel to each other andparallel to and surrounding said electrode assembly.

2. The tube defined in claim 1 wherein said magnet rods are external toand surround the tube envelope.

3. The tube defined in claim 1 wherein said magnet rods are mountedinside said envelope and surrounding said electrode assembly.

4. A magnetron beam switching tube having an electrode assemblyincluding a cathode and a plurality of groups of electrodes; each groupof electrodes including a target electrode which receives an electronbeam and produces an output signal therefrom, a spade electrode whichholds an electron beam on its associated target electrode, and aswitching electrode which serves to switch an electron beam from onegroup of electrodes to the next; and an array of magnet rods surroundingsaid electrode assembly.

References Cited in the file of this patent UNITED STATES PATENTS HewittNov. 11, 1919 Skellett June 3, 1941 Hoberg Oct. 21, 1958

